Acetaminophen Has Lipid Composition-Dependent Membrane Interactivity That Could Be Related to Nephrotoxicity but Not to Analgesic Activity and Hepatotoxicity.

<bold>Objective: </bold>Although acetaminophen is one of the most widely used over-the-counter drugs, the mechanisms by which this classical drug exerts analgesic, hepatotoxic, and nephrotoxic effects remain unclear. We hypothesized that acetaminophen might act on cellular membranes of nerves, liver, and kidneys. In order to verify this hypothesis, we studied the interactivity of acetaminophen with biomimetic lipid bilayer membranes by comparing with structurally related phenacetin.<bold>Methods: </bold>Liposomal membranes (unilamellar vesicles suspended in the buffer of pH 7.4) were prepared with phospholipids and cholesterol to mimic the membrane lipid composition of neuronal cells, hepatocytes, and nephrocytes. They were subjected to reactions with acetaminophen and phenacetin at clinically relevant concentrations, followed by measuring fluorescence polarization to determine their membrane interactivity to modify membrane fluidity.<bold>Results: </bold>Acetaminophen and phenacetin interacted with neuro-mimetic and hepato-mimetic membranes to increase membrane fluidity at 10-100 μM. Both drugs were more effective in fluidizing hepato-mimetic membranes than neuro-mimetic membranes. Although the relative membrane-interacting potency was phenacetin >> acetaminophen in neuro-mimetic and hepato-mimetic membranes, such membrane effects conflicted with their relative analgesic and hepatotoxic effects. Acetaminophen and phenacetin strongly interacted with nephro-mimetic membranes to increase membrane fluidity at 2-100 μM and 0.1-100 μM, respectively. Phenacetin interacted significantly with nephro-mimetic membranes at lower concentrations (<2 μM) than acetaminophen, which was consistent with their relative nephrotoxic effects.<bold>Conclusion: </bold>In comparison with phenacetin, lipid composition-dependent membrane interactivity of acetaminophen could be related to nephrotoxicity but not to analgesic activity and hepatotoxicity. [ABSTRACT FROM AUTHOR]